Organic solar cells (OSCs) are expected to attain a satisfactory power conversion efficiency (PCE) and acceptable production cost to guarantee strong competitiveness. However, state-of-the-art PCEs are all achieved by polymer donors with halogen atom-based active layers, which leaves room for researchers to develop efficient systems without the currently widely used halogenated polymer donors. Here, we combined a recent well-known nonfullerene acceptor (NFA) Y6 with our previously proposed donor PBDTNS-BDD (possessing no halogen atoms) and successfully acquired a moderate PCE of 12.55%. By utilizing a classic ternary strategy of introducing a fullerene acceptor PC 71 BM into the blend, the PCE of the device is significantly increased to 14.88%, close to the 15% milestone. The improvement in the device performance due to PC 71 BM is attributed to the fact the improved blend morphology (molecular packing and domain size) enables suppressed exciton recombination and more efficient and balanced charge transport. Our work extends the applicable range of the classic ternary design of adding fullerene into an efficient NFA-based binary system, e.g., non-halogenated polymer:Y6 combination, to achieve a nearly 15% efficiency for its ternary device, providing new directions for applications of OSCs.

Traditional additives like 1,8-diiodooctane and 1-chloronaphthalene were successfully utilized morphology optimization of various polymer solar cells (PSCs) in an active layer, but their toxicity brought by halogen atoms limits their corresponding large-scale manufacturing. Herein, a new nontoxic halogen-free additive named benzyl benzoate (BB) was introduced into the classic PSCs (PTB7-Th:PC71BM), and an optimal power conversion efficiency (PCE) of 9.43% was realized, while there was a poor PCE for additive free devices (4.83%). It was shown that BB additives could inhibit PC71BM’s overaggregation, which increased the interface contact area and formed a better penetration path of an active layer. In addition, BB additives could not only boost the distribution of a PTB7-Th donor at the surface, beneficial to suppressing exciton recombination in inverted devices but also boost the crystallinity of a blend layer, which is conducive to exciton dissociation and charge transport. Our work effectively improved a device performance by using a halogen-free additive, which can be referential for industrialization.

A ternary strategy of halogen-free solvent processing can open up a promising pathway for the preparation of polymer solar cells (PSCs) on a large scale and can effectively improve the power conversion efficiency with an appropriate third component. Herein, the green solvent o-xylene (o-XY) is used as the main solvent, and the non-fullerene acceptor Y6-DT-4F as the third component is introduced into the PBB-F:IT-4F binary system to broaden the spectral absorption and optimize the morphology to achieve efficient PSCs. The third component, Y6-DT-4F, is compatible with IT-4F and can form an “alloy acceptor”, which can synergistically optimize the photon capture, carrier transport, and collection capabilities of the ternary device. Meanwhile, Y6-DT-4F has strong crystallinity, so when introduced into the binary system as the third component can enhance the crystallization, which is conducive to the charge transport. Consequently, the optimal ternary system based on PBB-F:IT-4F:Y6-DT-4F achieved an efficiency of 15.24%, which is higher than that of the binary device based on PBB-F:IT-4F (13.39%).

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A new alcohol‐soluble polymer PFN‐ID is successfully synthesized by combining N,N‐di(2‐ethylhexyl)‐6,6′‐dibromoisoindigo and an amino‐containing fluorene subunits, and applied to polymer solar cells (PSCs) with PTB7‐Th:PC71BM as an active layer. The n‐type backbone of the PFN‐ID improves electron transfer performance and thus optimizes device performance. The PSCs with PFN‐ID as cathode interfacial layers (CILs) have significantly improved compared to the device without the interface layer, especially the optimum power conversion efficiency (PCE) of PSCs reaches up to 9.24%, which is 1.62 times higher than that of devices without CILs. The I–V curves show that the introduction of the n‐type backbone leads to a significant increase in the conductivity of PFN‐ID compared to PFN. The UV photoelectron spectroscopy and Mott–Schottky curves further confirm that PFN‐ID can decrease the work function of Al electrode, and increase its built‐in potential, giving higher open‐circuit voltage. The resulting conventional PSCs using PFN‐ID as cathode interlayer achieve high photovoltaic performance, and the research results can provide a new strategy for the advancement of PSCs.